The invention relates to a method and a device for recognition of cassettes, such as different types of VHS video magnetic tape cassettes for example, for recording and/or replaying information, having a recording medium in the form of tape and having different playing times.
Although magnetic tape cassettes for television video recording and/or replay apparatuses, called video recorders in the following text, are externally of the same size, they can nevertheless have different playing times. For example, for VHS video recorders there are standardized tape cassettes having a total playing time of 30 minutes (E 30), 60 minutes (E 60), 90 minutes (E 90), 120 minutes (E 120), 180 minutes (E 180), 195 minutes (E 195), 210 minutes (E 210), 240 minutes (E 240) and 300 minutes (E 300) whichxe2x80x94as is illustrated in the following table for these various cassette typesxe2x80x94are implemented using two different reel core diameters D0 and three different tape thicknesses d or tape thickness ranges. In addition to these tape cassettes, there are also two further tape cassettes, which are intended to camcorders and have a playing time of 30 minutes (EC 30) and 45 minutes (EC 45), which are smaller externally and, as is known, can also be played in a video recorder by means of a so-called adaptor cassette.
For type recognition of such tape cassettes, it is known, for example from European Patent Application EP-A-0 216 260, for the instantaneous circumference of both tape reels, formed by the respective reel core and its instantaneous tape quantity, to be determined at a predetermined tape drive speed via a measurement of the time of revolution of the tape reels in order then to identify the cassette type used by forming the sum of the squares of the two instantaneous tape reel circumferences, with this sum subsequently being compared with a corresponding comparison value range which is provided in a comparator. The method is based on the sum of the respective area of the two tape reels being constant at any winding time. However, this method is unsuitable for unambiguous type recognition of tape cassettes having different playing times, in which the sum of the squares of the two instantaneous tape reel circumferences would overlap because of the different tape thickness d, such as cases where a E 180 or E 210 is used, for example, as well as in cases where a E 195 or E 240 is used.
It is furthermore known for the respectively used cassette type to be identified via a determination of the tape running time. Although this method, which is based on an exact measurement of the tape thickness d, also allows reliable indicator results in cases where an E 180 or E 210 and an E 195 or E 240 are used, a time of several minutes is required, however, for this purpose before the respective cassette type is identified.
It is thus the object of the invention to shorten the time for a reliable cassette-type indication in particular of all the tape cassettes which are used in a VHS video recorder.
This object is achieved by the features specified in claim 1 and claim 2. Advantageous developments of the invention are described in the respective subclaims.
The invention is based on the knowledge that, by interpretation of the tape thickness and tape quantity or tape length of the recording medium, even those cassettes can be distinguished and can thus be determined in the case of which the sum of the squares of the two instantaneous tape reel circumferences would entirely or partially overlap because of different tape thickness and tape length. In principle, one measurement for the tape thickness and one measurement for the tape quantity or tape length are in each case logically linked to one another for this purpose.
As a result of the fact that the respective cassette type can be recognized by logically linking these two different characteristic features, it is not necessary to determine these features exactly, which fact is used according to the invention for considerably faster tape identification of tape cassettes. A relatively rough determination of the tape thickness and/or the tape quantity of the recording medium is thus sufficient to be able to carry out a corresponding classification of the tape thickness or tape quantity predetermined by the respective cassette standard.
In addition, the method according to the invention has the advantage that it can be implemented, for example, by minor modification outlay to a circuit device, which is provided anyway for a recorder, for determining the tape running time.